1. Field
Embodiments of the disclosure relate generally to the field of surface geometries for aerodynamic improvements to aircraft or surfaces having a flow interface and more particularly to embodiments and fabrication methods for use of high elongation elastomeric materials to form aerodynamic riblets or other high-aspect-ratio surface microstructures requiring high durability.
2. Background
Increasing fuel efficiency in modern aircraft is being accomplished through improvement in aerodynamic performance and reduction of structural weight. Recent advances in the use of microstructures such as riblets on aerodynamic surfaces have shown significant promise in reducing drag to assist in reducing fuel usage. Riblets have various forms but advantageous embodiments may be ridge-like structures that can reduce drag in areas of a surface of an aircraft exposed to a turbulent boundary layer. The riblet ridges tend to inhibit turbulent motions involving lateral velocities, thus reducing the intensity of small-scale streamwise vortices in the lower part of the boundary layer, and thus reducing skin-friction drag.
In certain tested applications riblets have been pyramidal or inverted V shaped ridges spaced on the aerodynamic surface to extend along the surface in the direction of fluid flow. Riblet structures have typically employed polymeric materials, typically thermoplastic or thermoset polymers. However in service use such as on an aircraft aerodynamic surface, polymers are relatively soft thus reducing the durability of the surface. Existing solutions with polymeric tips may readily deform hundreds of percent with fingernail pressure and may be unrecoverable since the thermoplastic polymer (fluoropolymers such as THV or FEP for example) has “yielded” or the thermoset (structural epoxy for example) has fractured at relatively low strain. Thermoplastic or low-elasticity thermosets deform readily with a fingernail cross wise to the riblet ridges/grooves, either by plastic deformation or by cavitation and cracking. Such structures may be undesirable in normal service use on an aircraft or other vehicle. Additionally certain aircraft surfaces are required to withstand interactions with various chemicals including Skydrol®, a hydraulic fluid produced by Solutia, Inc.
The practicality of riblets for commercial aircraft use would therefore be significantly enhanced with a riblet structure providing increased durability and aircraft fluids compatibility.